Any prejudice that results in unfair treatment of an employee at work, such as denial of promotion, transfers, leaves etc. It may result from a variety of factors such as age, gender, sexuality, race, religion, caste, regionality, etc.
Bullying and discrimination at work may take many forms such as yelling in private and in front of other team members, drafting rude emails, having a condescending body language, denial of opportunity, harassment, unequal pay, social isolation, etc. Such actions cannot be normalised, and that is where the organisation steps in - to take action based on disciplinary procedures in place already, and to ensure such acts do not take place again/repeatedly. Effective and continual internal communications regarding the same also convey the seriousness of the issue, and reinforces your company's commitment to being equal and just.